I’ve reused tons of jigs between different sessions, on/off cycles etc.
You need a pretty solid reference point to place the jig. I use 12x20” jigs also.
So I made crumbtray rulers and align the jig to that. I used a line of tape before that. Either works.
Then, make a 12x20 artboard in your design program.
Set your design up in the design program.
Your jig circle would be one color so it’s a separate operation.
Upload the file. Cut the circle out. Run your engrave.
For any new files, just open your jig template, align the artwork, save a copy and upload the copy. Put your jig back in to the same place it was before and run your new engrave.